Supervision is one of the core operations that an Actor can fulfill. Handling errors is not always easy in a classic object oriented programming context as exceptions can be difficult to predict as they are fully embedded in the normal execution flow. In the Akka Actor Model, errors are handled in a well-structured isolated execution… Continue reading How to Supervise Akka Actors
Actors are a really powerful tool to handle concurrency thanks to their message-based model. However, they can be tricky to test: sending and processing messages is done asynchronously. Moreover, their status is hidden internally and it cannot be easily accessed to make assertions on it. The Akka Team has created a library, called akka-testkit, to… Continue reading How to test Actors with Akka TestKit and Spec2
Spray is a library written on top of Akka and Scala that allows to quickly create REST interfaces. It is becoming more and more popular in the Scala community because it is easy to use and performant thanks to this asynchronous, actor-based model. This article describes how to efficiently exploit Spray to create a simple… Continue reading How to build a REST api with Spray and Akka
Scala has adopted many concepts from other functional programming languages: higher-order functions from Haskell, actors model from Erlang, futures from Clojure, etc. However, Scala has also introduced new tools in the functional programming world: case classes is one of them. Case classes are a special type of classes, as the compiler automatically adds some useful… Continue reading How to use Case Classes in Scala
Actors are components of message-passing systems that are particularly popular these days. They make concurrency a lot easier to understand compared to the traditional thread-monitor-lock model. An actor is a thread-like program that run independently from other actors. It has a mailbox to receive messages from other actors, where each message represents a task to… Continue reading Akka Actors: Best Practices
The following article provides a list of all the different type parameterisations available in Scala and how to use them. Variance A class can depend on a type constructor. The following is an example trait that depends on a generic type T: The above declaration implies that the generic type T is the only valid… Continue reading Type Parameterisation
Scala implicits are a great tool to remove code duplication and convert objects from different domains. However, we need to learn not to abuse them: by hiding code they can make the code more concise but more cryptic at the same time. In order to use implicits efficiently, we need to know how the compiler tries… Continue reading Implicits: Rules and Applications
REST APIs are becoming more and more popular: they allow horizontal scalability, they are flexible to change and easy to use without the need of detailed documentation. However, some APIs claim to be RESTful when they are not. This is mainly for two reasons: - We don’t always have a clear idea of what RESTful means, we just associate… Continue reading RESTful now more important than ever.
Sometimes we want to hide/protect our variables — the classic concept of encapsulation in object oriented programming. We’d like to write a Scala class to manage someone’s age. In particular, we’d like to: - lie on our age if we are not teens anymore (you never know!) - put some validation to avoid negative age values Our… Continue reading Stateful objects: use them to lie!
Scala uses access modifiers quite differently from Java. Let’s see what the differences are and why qualified access modifiers are so powerful in Scala. default access modifier Scala >> public Java >> protected While in Scala the public keyword doesn’t exist, Java allows you to explicitly use the keyword protected as you please. private Scala >> accessible from a class and its companion… Continue reading Super Powers to Qualified Access Modifiers